HOLMES MILL, Ky. — Mine safety officials say a sealing material used at a Kentucky mine where an explosion killed five miners is an easy and cost-effective way to contain combustible gases, but others in the industry say convenience comes at a cost.

Critics say the material, similar to plastic foam, should be banned. Rescuers reported that the seals did not withstand Saturday’s blast at the Kentucky Darby Mine No. 1.

The foam blocks out methane and other gases that occur naturally in previously mined areas and often are used instead of concrete blocks.

But now officials are trying to determine whether the foam seals work as well as concrete.

“That’s the question: Are these things leakier than concrete blocks?” Chuck Wolfe, spokesman for the state Environmental and Public Protection Cabinet, said Tuesday. He also wondered whether the sealing has been performed properly at mines that use the alternative blocks.

Mine operators like to use the foam seals because they are cheaper and lighter than concrete, Wolfe said.

But Tony Oppegard — former general counsel for the Kentucky Department of Mines and Minerals, who now represents coal miners — said the alternative seals endanger miners.

“We don’t believe (alternative seals) can withstand the pressure of an explosion as the concrete ones do,” Oppegard said.

The alternative blocks failed in both the Darby mine and the Sago Mine in West Virginia, where a January explosion killed 12, and now officials are asking whether federal regulators should raise the threshold for alternative seals.

Alternative seals are common, but most coal operators still use concrete, said Chris Hamilton, head of the West Virginia Coal Association and a member of a mine safety task force assembled after the Sago disaster.

Late Monday, the federal Mine Safety and Health Administration said it would require concrete seals while the issue is reviewed. Kentucky Gov. Ernie Fletcher, who visited the area Tuesday, said thousands of such seals may be in use.

Federal and state investigators entered the Darby mine Tuesday. Concerns about flammable methane and poisonous carbon monoxide gases had kept them out until its ventilation system could be repaired and the gases were brought to safe levels.

The mine was cited 41 times in the past five years for not cleaning up coal dust and other combustible materials, including three times this month, according to the MSHA.

But Wolfe said Tracy Stumbo, the state’s chief investigator, “has seen nothing to indicate coal dust was a factor. He considers it a methane explosion.”

Kentucky Darby officials have declined to comment since the explosion Saturday. A call to the company’s mine office was not answered Tuesday.

Since Kentucky Darby LLC took over as operator of the mine in May 2001, there had been 10 injuries but no deaths until Saturday’s blast.

Three of those killed — Paris Thomas Jr., 35; Roy Middleton, 35; and George Petra, 49 — survived the initial blast but died of carbon monoxide poisoning, according to preliminary tests. Amon Brock, 51, and Jimmy D. Lee, 33, died of blunt force and heat injuries.

The three who died of carbon monoxide poisoning were wearing their self-rescuer air packs when their bodies were found, the governor said. The packs had been activated, rescuers said.

Whether the air packs were working properly remains part of the investigation, Fletcher said.

The men in the Kentucky mine were using the same air pack model as the Sago Mine disaster victims, even though the lone survivor had questioned the devices’ reliability about a month ago.

On Tuesday, the wife of the sole Sago survivor called for answers about the air packs.

“There is a problem,” Anna McCloy, wife of Randal McCloy Jr., said in a statement. “We need more answers than, ‘We tested them and they worked.’ We can’t continue to send miners into the mines with a false promise that these rescuers are going to work when they need them the most.”

On Tuesday, a water truck operator was killed when the vehicle went over an embankment and crashed at a mountaintop coal mine in Breathitt County in eastern Kentucky, said Mark York, spokesman for the Kentucky Cabinet for Environmental and Public Protection.

The national death toll from coal mining accidents this year, including Tuesday’s fatality, is 32, up from 22 in 2005.

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